1. Field of the Invention
The present invention relates to a conveying apparatus mounted in a recording apparatus to convey sheets.
2. Description of the Related Art
One type of conveying apparatuses used in recording apparatuses picks up a plurality of sheets one by one that are stacked in a paper feed tray in the front portion of the recording apparatus and inverses the conveying direction of the sheets using a curved conveyance path (hereinafter, referred to as “U-turn path”) to convey them to a recording unit of the recording apparatus. An image reading and recording apparatus that uses such a conveying apparatus is discussed in Japanese Patent Application Laid-Open No. 2010-150030. Hereinafter, the conveyance to pass sheets through such a U-turn path is referred to as “U-turn conveyance.”
The sheets, which are picked up from the paper feed tray and conveyed to the recording unit, pass the U-turn path one by one. Sheets having higher stiffness cannot be conveyed along the shape of the U-turn path, resulting in jamming of the sheet, or resistance against the sheet conveyance is generated due to increase in friction between the sheets and the U-turn path.
If a conveyance resistance is large, for example, when a feeding roller has a power insufficient to successfully convey the sheet from the paper feed tray to the recording unit, slippage occurs between the feeding roller and the sheets. If an output from a drive source of the feeding roller is not large enough, the feeding roller cannot receive a driving force that overcomes the conveyance resistance, making the sheets jammed within the U-turn path. In addition, other troubles may occur, such as buckling of the sheets because the sheets cannot endure the conveyance resistance from the U-turn path and the compression force due to the conveying force of the feeding roller.
Accordingly, in a conveying apparatus that utilizes U-turn conveyance, a feeding roller is arranged upstream of a U-turn path in the conveying direction of sheets, and also one or more intermediate rollers are arranged within the U-turn path as needed. The intermediate rollers disposed near the curved portion of the U-turn path allow sheets to be conveyed in the direction along a shape of the U-turn path.
FIG. 18 schematically illustrates arrangement of conveyed sheets and an intermediate roller pair. In FIG. 18A, a first roller 1001 protrudes in a large amount from a guide surface. In FIG. 18B, a first roller 1001 protrudes in a small amount from a guide surface. FIG. 18 illustrates only apparatus members necessary for description. FIG. 18 does not illustrate an inner guide that forms the U-turn path and is located in the curving direction (i.e., on the inner periphery side) of a U-turn path, but illustrates only an outer guide opposite the inner guide (i.e., on the outer periphery side).
The first roller 1001 and a second roller 1002 form an intermediate roller pair located in the U-turn path. An upstream guide 1005 is disposed upstream, and a downstream guide 1004 is disposed downstream in the sheet conveying direction of the intermediate roller pair. The arrow 1007 in FIG. 18 illustrated by a solid line indicates a sheet conveying direction along which sheets are conveyed to the intermediate roller pair, and the arrow 1003 illustrated by a broken line indicates the nip direction of the intermediate roller pair.
The nip direction herein is oriented perpendicular to a straight line between the rotation axes of two rollers 1001 and 1002 within a cross section surface perpendicular to the rotation axes of the two rollers 1001 and 1002. In addition, the nip direction extends from an upstream to downstream side of the intermediate roller pair. An extended plane 1011 from the upper surface of the upstream guide 1005 forms an approach angle 1008 with a tangent 1010 running on the intersection between the extended plane 1011 and the surface of the first roller 1001. The first roller 1001 produces an amount of protrusion 1006 from the extension of the plane 1011 of the upper surface in the upstream guide 1005.
When a sheet is conveyed by a feeding roller (not illustrated) to the U-turn path, the sheet's leading edge is caused to advance subject to its stiffness along the outer guide. Thus, the sheet advances along the upstream guide 1005 in the direction illustrated by the arrow 1007. As illustrated in FIG. 18A, if the sheet conveying direction 1007 forms a large angle 1009 with the nip direction 1003, the approach angle 1008 relative to the first roller 1001 becomes large. In this case, before the sheet is drawn into the nip between the intermediate roller pair, the sheet's leading edge collides against the first roller 1001, which may cause damage to the sheet's leading edge or failure in conveyance, for example, the sheet is not drawn into the nip.
In order to reduce the collision impact of the sheet against the first roller 1001 without changing the angle 1009 between the sheet conveying direction 1007 and the nip direction 1003, as illustrated in FIG. 18B, the amount of protrusion 1006 of the first roller 1001 needs to be reduced as compared to the case in FIG. 18A. As the amount of protrusion 1006 is reduced, the approach angle 1008 of the sheet to the first roller 1001 is reduced. However, in this case, it is also likely that the sheet collides against the second roller 1002 before reaching the nip between the intermediate roller pair. Accordingly, this case also tends to cause failure in conveyance of sheets.
Therefore, in order to make a sheet's leading edge smoothly drawn into the nip between the intermediate roller pair, when the intermediate roller is arranged within the U-turn path, it is desirable that the nip direction 1003 of the intermediate roller pair is similar to the sheet conveying direction 1007 in the upstream side of the intermediate roller pair.
In conveying the sheets using the intermediate roller pair, if the nip direction 1003 of the intermediate roller pairs is almost perpendicular to the surface of the downstream guide 1004 (see FIG. 19A), the sheet conveying direction 1007 needs to be significantly bent. As a result, the conveyed sheet needs to be bent in a large amount. Hence, the amount of bending of the sheet is smaller in the structure (see FIG. 19B) where the nip direction 1003 of the intermediate roller pair follows the curved U-turn path (in a direction to the inner side). The larger an amount of bending of a sheet, the larger friction between the sheet and the U-turn path due to stiffness of the sheet, which leads to increase in conveyance resistance. Accordingly, to avoid the conveyance resistance, it is desirable to arrange the nip direction 1003 of the intermediate roller pair to follow the curved U-turn path.
However, it is very difficult to arrange the nip direction 1003 of the intermediate roller pair within the curved U-turn path to satisfy the above two conditions.
To solve the problem, for example, a plurality of intermediate roller pairs can be arranged within the U-turn path such that the nip directions of each intermediate roller pair are changed little by little. However, this method increases the number of rollers, increasing manufacturing cost and size of the conveying apparatus.
Alternatively, the nip pressure of an intermediate roller pair can be increased to enable conveyance of sheets despite of conveyance resistance from the U-turn path. However, this method increases the load on a driving unit that drives intermediate rollers, or tends to cause troubles such as deformation of components that support the rollers, which require a larger power source for the driving unit and enhancement of the strength of the roller supporting components. As a result, the increase in nip pressure also increases manufacturing cost as in the above case.